Conductor Mariss Jansons This week, listeners can see for themselves how the area’s hometown orchestras, all featured below, measure up against the orchestra considered by many to be the finest in the world. Also, a months-long festival of American music — with lots of free concerts to hear — kicks off this weekend. BATTLE OF THE ORCHESTRAS: >> Amsterdam’s Royal Concertgebouw Orchestra often appears at or near the top of lists of the world’s…